Vehicle anti-skid braking apparatus having two modes of operation

ABSTRACT

A valve for an antiskid braking system of the type in in which there is a source of braking pressure connectable to the brakes by means of a valve arrangement controlled by a device which is sensitive to the dynamic state of the wheels of the vehicle to connect the brakes to a discharge conduit if the wheels approach a state of incipient skid, the discharge conduit leading to a valve which is sensitive to the braking pressure to release the brakes in one of two different ways depending on the braking pressure which exists when the state of incipient skid arises. The valve means includes a communication part between an inlet and an outlet port, with a valve shutter biased by a spring to a first position against a shoulder of the port, in which position fluid flow is allowed by grooves in the face of the shutter and by a flexible rim the shutter is movable against the action of the spring to shut off the communication port if the braking pressure exceeds a predetermined threshold.

United States Patent 1 Peruglia VEHICLE ANTI-SKID BRAKING APPARATUSHAVINGTWO MODES OF OPERATION Marco Peruglia, Turin, Italy 52 us. c1.303/21 F,l88/l8lA, 303/68, 303/69 51 1111. C1. B60t 8/06 [58] FieldofSearch ..303/21,61-63, 303/68-69; 188/181 [56] References Cited UNITEDSTATES PATENTS 3,695,734 10 1972 Hennig etal. 303 21 F 3,717,385 2/l973'Michellone 303/21 F 1 Primary Examiner-Duane A. Reger AssistantExaminer-D. C. Butler Attorney-Richard C. Sughrue et al.

[ Oct. 23, 1973 [57] ABSTRACT A valve for an antiskid braking system ofthe type in in which there is a source of braking pressure connectableto the brakes by means of a valve arrangement controlled by a devicewhich is sensitive to the dynamic state of the wheels of the vehicle toconnect the brakes to a discharge conduit if the wheels approach a stateof incipient skid, the discharge conduit leading to a valve which issensitive to the braking pressure to release the brakes in one of twodifferent ways depending on the braking pressure which exists when thestate of incipient skid arises. The valve means includes a communicationpart between an inlet and an outlet port, with a valve shutter biased bya spring to a first position against a shoulder of the port, in whichposition fluid flow is allowed by grooves in the face of the shutter.and by a flexible rim the shutter is movable against the action of thespring to shut off the communication port if the braking pressureexceeds a predetermined threshold.

3 r3-33.9l inlsimsaine$59595.-. H 3.

VEI-IHCLIE ANTI-SKID BRAKING APPARATUS HAVING TWO MODES OF OPERATIONBACKGROUND OF THE INVENTION The present invention relates to a pneumaticantiskid braking system for motor vehicles, and particularly to a systemof the type which is capable of operating in two different modes independence on the degree of adhesion between the tires and the surfaceover which the vehicle is moving.

The reasons why two modes of operation are desirable are fullyillustrated in previous Patent Applications by the same Applicant, inparticular Italian 'Pat. application 71335 A/70 and 69531 A/7lmay bereferred to for a description of two different solutions of the problemsinvolved. 1

it is known that the rate of release of braking pressure during theantiskid action of a braking system should be different when a vehicleis travelling upon a, slippery surface, such as an icy road, from thatwhich is required upon a surface with a good adhesion, such as a hard,dry, surface. In the case ofa slippery surface it is necessary for thepressure to drop rapidly to zero as soon as a control device, which issensitive to the dynamic state of the wheel, operates in response toanincipient skid, whereas in the case of a hard, dry surface of goodadhesion a fixed drop in the braking pressure followed by a gradual dropto a threshold value, with a final decrease down to zero from thisthreshold is required.

The Italian Pat. Application 69531 A/7l mentioned above describes adevice consisting of a set of valves capable of switching from one modeof operation to another by means of a shutter with a throttle orificewhich assumes one of two positions corresponding to the two modes ofoperation of thedevice, depending upon the pressure in the brake fluidand the pressure exerted by a calibrated spring set at threshold.

This earlier device, although effective, is not very sensitive,responding to pressures within ranges of operative pressures in a bandon either side of the threshold pressure of the spring, rather than to adiscrete pressure.

In fact, the dynamic action to which the shutter is subjected bypressures only slightly greater than the threshold pressure could bediminished due to the throttle orifice so that upon surfaces of mediumadhesion, or during a traverse from a surface of good adhesion to one ofpoor adhesion (or vice versa) the antiskid system may not succeed inoperating in the best possible manner.

OBJECTS OF THE INVENTION The object of the present invention is toprovide a device which is more sensitive than the one mentioned above sothat the antiskid system behaves in every case in a preciselypredetermined way, especially at levels of operating pressure which areonly slightly greater than the threshold pressure, and in which theshutter rapidly moves in the way it should in order to produce thedesired result.

SUMMARY OF THE INVENTION According to the present invention there isprovided a pneumatic antiskid braking device for at least one wheel of avehicle, comprising a source of braking pressure and a braking deviceconnectable to one another by valve means controlled by a detectordevice which is sensitive to the dynamic state of the wheel, andoperable to establish communication between the source of brakingpressure and the braking device when the wheel is in a normal dynamicstate, and to establish communication between the braking device and adischarge conduit when the wheel is in a state of incipient skidding,the discharge conduit being connected to an inlet port of valve meanssensitive to the braking pressure, the valve means including a firstcommunication port between the said inlet port and an absorber, and asecond communication port between the said inlet port and a dischargeport which communicates with the atmosphere, the inlet port being alwaysin communication with the first communication port and being always incommunication with the discharge port to the atmosphere through a fixedthrottle orifice, characterise d in that the second communication portis closable by the movement of a shutter which is normally kept in afirst positionin which one face of the base thereof rests against anannular seat, by a calibrated spring and which is movable to a secondposition in which the other face of the base thereof rests against anannular valve seat to prevent fluid flow through the said secondcommunication port when the braking pressure exceeds a predeterminedthreshhold set by the calibrated spring, passage of the fluid beingpermitted, when the shutter is in the said first position, by a numberof grooves in the base of the shutter and also by the rim of the shutterbeing flexible.

One advantage of such a system is that the throttle orifice can beadjusted to adapt the system to particular uses, whereas in thepreviously known devices, such as that described in Italian Pat.Application 695 31 A/71 an adjustment of this type is obviously notpossible.

The required flexibility of the said walls of the shutter is preferablyachieved by making the shutter of rubber or ofa synthetic material ofsimilar elastic characteristics.

Other features and advantages of the invention will become more apparentfrom the following description, which is provided purely by way ofexample.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partly schematic diagramof an antiskid braking device formed as one embodiment of the invention;

FIG. 2 is a graph illustrating the variation of the braking pressure ofthe embodiment of FIG. 1 in one mode of operation;

FIG. 3 is a graph illustrating the variation of the braking pressure ofthe embodiment of FIG. 1 in the other mode of operation; and

FIG. 4 is a diagram showing the outer base of the shutter of theembodiment of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 thereis shown a source it) of pneumatic pressure, which is controlled bymeans of a pedal 12. The pressure source ltl applies pneumatic fluid toa braking device 14 of a vehicle (not shown) by means of a three-wayelectrically operated valve 16 via a conduit 18. The electricallyoperated valve 16 will be termed hereinafter an electrovalve.

A control device 24! which is sensitive to the dynamic state of a wheelof the vehicle, and which may be of any suitable known type, controlsthe switching of the elctrovalve 16 when the wheel (not shown) enters anincipient skid state, to place the conduit 18 in communication with anoutlet conduit 22, and to cut off communication between the source ofpressure 10 and the braking device 14.

The outlet conduit 22 is connected to an inlet port 26 of a valvearrangement 24; the port 26 communicates permanently, through apassageway 28, with an absorber chamber 30, and is also able tocommunicate with a cylinder 32, formed in the casing of the valve, bymeans of a number of grooves 34 (FIG. 4) in the base of a cup-shapedshutter 36. The base of the shutter 36 is pressed against an annularseat 40, formed by a shoulder in the cylinder 32, by one end of athreshold spring 42 one end of which abuts the inside bottom 44 of theshutter 36, and the other end of which abuts the base of a plug 46 whichis received in the casing of the valve 24. The plug 46 is provided witha throttle orifice 48 and with a port 50 both of which are open to theatmosphere, and both of which communicate with a chamber 32 and is heldin place by a circlip 52. The shutter 36 can be moved against the actionof the spring 42 until the inside base 44 abutss the plug 46 and closesthe port 50.

Thus, in a case in which the braking pressure, that is the pressure ofthe fluid in the brake cylinders, is less than the threshold value ofthe spring 42, when the antiskid control device 20 operates theelectrovalve 16 switches an air enters the valve 24 through the part 26,passes into the chamber 32, through the grooves 34 in the outside base40 of the shutter 36, forces its way past the resilient lateral walls ofthe shutter 36, and finally discharges freely into the atmosphere viathe outlet port 50. The line ABC of FIG. 2 illustrates the pressurevariation in this first mode of operation.

Referring now to FIG. 3, it will be supposed that the braking pressurehas reached a value above P the threshold value of the spring 42 whenthe antiskid control device 20 operates to control the release of thebrakes the fluid under pressure travels to the inlet port 26 of thevalve 2d and on arrival moves the shutter 36 sharply towards the plug 46against the force exerted by the spring 42, so that subsequent dischargeto the atmosphere can only take place through the throttle orifice 48.

The braking pressure will thus discharge initially into the absorber 30,causing a first rapid drop'in the braking pressure, as shown by the lineEF of FIG. 3, the pressure will then continue to fall as the fluid isdischarged through the throttle orifice 48 until it reaches pressureP,,, as shown by the line FG; at this point the force of the spring 42overcomes the force exerted by the pressure of the fluid on the base ofthe shutter 36 forces the shutter 36 back against the annular seat 40:the fluid will thus discharge freely to the atmosphere, forcing its waypast the elastic walls of the cup 36 and entering the port 50.

It will be appreciated that an arrangement of this sort will ensureperfect operation of the antiskid device whatever the pressure in thebraking fluid, and with a high response speed.

We claim:

1. In a pneumatic antiskid braking system for at least one wheel of avehicle, comprisng a source of braking pressure,

braking means operating on said wheel of said vehicle,

first valve means interconnecting said source of braking pressure andsaid braking means,

a discharge conduit connected to said first valve means,

detector means sensitive to the dynmaic state of said wheel of saidvehicle,

means connecting said detector means to said first valve means such thatsaid first valve means establishes communication between said source ofbraking pressure and said braking means when said wheel is in a normalstate and establishes communication between said braking means and saiddischarge conduit when said wheel is in an incipient skid state,

second valve means connected to said discharge conduit, said secondvalve means including an inlet port, an absorber, a first communicationport between said inlet port and said absorber, a discharge port whichcommunicates with the atmosphere, a second communication port betweensaid inlet port and said discharge port, and a throttle orifice, saidinlet port being always in communication with said absorber via saidfirst communication port and always in communication with said dischargeport via said throttle orifice,

the improvement wherein there is provided,

a valve shutter and a valve seat in said second communication port, saidshutter being biased away from said valve seat by a biasing spring to afirst position where it abuts a shoulder in said second communicationport,

a plurality of grooves in the face of said shutter which abuts saidshoulder and a flexible rim to said shutter allowing fluid flow fromsaid inlet port to said discharge port when said shutter is in saidfirst position, said shutter moving to a second position to close saidcommunication port when said braking pressure exceeds a predeterminedthreshold value.

2. The antiskid braking system of claim 1 wherein said shutter is madeof an elastic material selected from the group comprising, rubber andsynthetic elastomeric materials.

3. The antiskid braking system of claim 1 wherein said shutter iscup-shaped.

# rs a 1 FORM PO-1050 (IO-69) Patent No. 3,767,273 Dated October 2 1973In entor( Marco It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Foreign Application Priority Data October 12, 1971 Italy 70339-A/71(SEAL) Attest:

0. M RSHALL ,DAN N Gommissioner of Patents EDWARD 1-1.FLET0HER,JR. Attesting Officer

1. In a pneumatic antiskid braking system for at least one wheel of avehicle, comprising a source of braking pressure, braking meansoperating on said wheel of said vehicle, first valve meansinterconnecting said source of braking pressure and said braking means,a discharge conduit connected to said first valve means, detector meanssensitive to the dynamic state of said wheel of said vehicle, meansconnecting said detector means to said first valve means such that saidfirst valve means establishes communication between said source ofbraking pressure and said braking means when said wheel is in a normalstate and establishes communication between said braking means and saiddischarge conduit when said wheel is in an incipient skid state, secondvalve means connected to said discharge conduit, said second valve meansincluding an inlet port, an absorber, a first communication port beTweensaid inlet port and said absorber, a discharge port which communicateswith the atmosphere, a second communication port between said inlet portand said discharge port, and a throttle orifice, said inlet port beingalways in communication with said absorber via said first communicationport and always in communication with said discharge port via saidthrottle orifice, the improvement wherein there is provided, a valveshutter and a valve seat in said second communication port, said shutterbeing biased away from said valve seat by a biasing spring to a firstposition where it abuts a shoulder in said second communication port, aplurality of grooves in the face of said shutter which abuts saidshoulder and a flexible rim to said shutter allowing fluid flow fromsaid inlet port to said discharge port when said shutter is in saidfirst position, said shutter moving to a second position to close saidcommunication port when said braking pressure exceeds a predeterminedthreshold value.
 2. The antiskid braking system of claim 1 wherein saidshutter is made of an elastic material selected from the groupcomprising, rubber and synthetic elastomeric materials.
 3. The antiskidbraking system of claim 1 wherein said shutter is cup-shaped.